During the Democrats’ Thursday evening debate in New Hampshire, Sen. John Kerry (Mass.) reiterated a point he has been making for months — that he is the strongest Democratic opponent for President Bush.

Kerry’s view was held by a plurality of Democrats who participated in the Iowa caucuses, according to an entrance poll conducted by a consortium of media companies. [IMGCAP(1)]

Among the 26 percent of caucus participants who said that the ability to beat Bush was foremost in their minds in deciding whom to support at the caucuses, 37 percent caucused for Kerry, 30 percent caucused for Sen. John Edwards (N.C.), 21 percent caucused for former Vermont Gov. Howard Dean and a mere 6 percent caucused for Rep. Richard Gephardt (Mo.).

But there was little or no empirical evidence at that time — or even now — that Kerry would be any stronger against Bush than his Democratic rivals. (This could, of course, change in the days and weeks ahead.)

In fact, four surveys conducted in early January (by Newsweek, Fox News/Opinion Dynamics, CNN/Time and the Pew Research Center) showed Bush holding statistically identical leads over Kerry, Dean, Edwards, Gephardt, Sen. Joe Lieberman (Conn.) and retired Gen. Wesley Clark.

Newsweek’s Jan. 8-9 poll, for example, showed the president leading Dean by 8 points, Clark by 9, Kerry and Lieberman by 11 and Edwards by 16. Bush’s lead was narrowest at 7 points over Gephardt, who is now out of the contest.

Indeed in Iowa, a Research 2000 poll conducted less than two weeks before the caucuses, Bush also held nearly identical leads over the six Democrats tested in hypothetical ballot tests. Again, in a further irony, Gephardt ran best against Bush.

But it isn’t only those numbers that raise questions about Kerry’s appeal, as well as whether Kerry’s nomination would have a more positive impact on the Democratic Party and the party’s other candidates. There is Kerry’s “Massachusetts problem.”

Any Democrat who comes from the Bay State — the state that gave America Michael Dukakis and Sen. Edward Kennedy — is going to have to prove to the rest of the country that he isn’t a “tax-and-spend liberal.”

It isn’t by coincidence, after all, that the last three Democratic presidents have been from the South. Kerry isn’t even from South Boston.

And after 20 years in the Senate, Kerry has a voting record a mile long. That record includes votes on taxes, same-sex marriage, defense spending and guns that Republicans will use to keep “red states” red.

Some Democrats have already breathed a sigh of relief at the prospect that Kerry, and not Dean, may be at the top of the ticket. But going from Dean to Kerry could be like jumping from the frying pan into the fire for Democrats involved in down-ballot races.

If you are a Democrat running for the Senate in the Carolinas, Georgia, Oklahoma, South Dakota or Alaska, does it make a heck of a lot of difference whether your name is immediately under Dean’s or Kerry’s? I’m not so sure.

Will Kerry be more of a help than Dean to House Democrats seeking to hold vulnerable seats in Texas, Louisiana or Kentucky? Unlikely.

Imagine what the Republicans could do to paint a picture of the Democrats if they nominate a Massachusetts Senator at a Boston party convention. It ain’t pretty.

So how did Iowa Democrats and others conclude that Kerry is the “most electable,” especially since at one time or another each of the top-tier Democrats has tried to make that case? I’m not sure. It may simply be a process of elimination.

Dean suddenly seemed too liberal to many, while Edwards still looks too young. Clark was an unknown quantity in Iowa, while Gephardt apparently was regarded as yesterday’s news.

So that leaves Kerry — tall, lots of hair, sufficiently dynamic, experienced and insisting over and over that the Republicans intend to make the 2004 election about national security and patriotism, issues on which he deems himself to be credentialed and inoculated from GOP attacks.

Yes, Kerry has assets, the foremost of which is that he has been tested politically, most recently in a tough 1996 Senate race against William Weld (R). And, Unlike Dean, Kerry voted for the Iraq war.

But the Massachusetts Senator’s long-term problems aren’t all that different than Dean’s. He can appear arrogant, has a voting record that would give Bush plenty of ammunition (indeed, one that is much more liberal than was Dean’s in Vermont) and has the New England albatross around his neck.

National Journal rated Kerry’s voting record for 2002 as the ninth most liberal in the Senate, more liberal than the records of Sen. Barbara Mikulski (D-Md.), Sen. Charles Schumer (D-N.Y.) or Sen. Tom Harkin (D-Iowa). You can bet the White House knows Kerry’s record well.

If Kerry becomes the Democratic nominee for president, he’ll probably run a good, competitive campaign. He might win. But it isn’t clear at the moment that he would be the strongest challenger to Bush, or that he would be less of a drag for Democratic candidates running in “red districts” or “red states.”

Early last week, Democratic National Committee Chairman Terry McAuliffe said that his party’s presidential nominee will become the “messenger” for the party. McAuliffe, of course, is correct. But Kerry’s message — both the one that he offers and the one that the Republicans will put into his mouth — seems to have at least as many vulnerabilities as Dean’s.

Stuart Rothenberg is editor of the Rothenberg Political Report.